It's really simple, I believe they serve up their videos with Flash which your tablet doesn't support. Flash for video isn't going away yet in many cases because HTML 5 video is still lacking all of the security features sites like this one require. So they did the next best thing, they built a custom app for your platform which gave them the security they desired and you a full user experience.
Edit: Just confirmed I can watch their videos on my Android tablet, thus it's just a lack of Flash that caused this. In fact on my ASUS Slider they are playing perfectly.
Edit: Just confirmed I can watch their videos on my Android tablet, thus it's just a lack of Flash that caused this. In fact on my ASUS Slider they are playing perfectly.